To: linux-wireless@vger.kernel.org
From: J Mo <jmomo@jmomo.net>
Subject: wpa_supplicant bridging problems
Message-ID: <56C3E95A.7080104@jmomo.net> (sfid-20160217_043544_707135_DE803A92)
Date: Tue, 16 Feb 2016 19:30:34 -0800
MIME-Version: 1.0
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Sender: linux-wireless-owner@vger.kernel.org


Hello everyone

I am having a very difficult time with a wireless bridging problem.

My objective is to use a Debian GNU/Linux host as a wireless ethernet 
bridge between itself, some hosts connected through a switch on it's 
eth0 port, and an OpenWRT router.

I have a test setup consisting of a laptop, a small PC (802.11 client), 
and the OpenWRT AP/router.

The wifi client system is an amd64(intel) with one 802.11 interface and 
a 1000BASE-T interface. The 802.11 hardware here is an Intel 3160. The 
OS is Debian GNU/Linux unstable with kernel 4.3.0-1-amd64 and 
wpasupplicant package version 2.3-2.3.

The 802.11 AP is a TP-Link TL-WR710N which is based off the Atheros ar9331.


My problem is the moment I bridge the wlan0 interface on the 802.11 PC 
client, wpa_supplicant stops doing it's job. It stops responding to any 
EAPOL frames from the AP, even though it seems to be receiving them.

It is noteworthy that the bridging works. I am able to get a DHCP lease 
on the laptop from the OpenWRT AP/router via bridging though the PC. 
Traffic passes both way and everything works great until the next WPA 
rekey event comes along (every 10 minutes by default for OpenWRT), and 
then the client gets deauth'ed from the AP because it fails to respond.

The only way I can get this to work is to first bring up my wlan0 
interface on the PC so that wpa_supplicant authenticates itself 
correctly. Once the 802.11 layer 2 is up, I manually use brctl to bridge 
in the eth0 and wlan0 ports on the PC. Everything works fine until the 
AP wants to rekey or the client needs to re-auth for some reason.


Here is what my setup looks like:

The OpenWRT device setup is pretty standard. The only thing required for 
the bridging is the addition of the "option wds 1" parameter under the 
wifi-iface in the "wireless" config file. The wds parameter enables 
4-address frames to allow the bridging. In case it's relevant, I'm doing 
WPA2 PSK AES/CCMP.

My PC/client /etc/network/interfaces file looks kind of like this:

allow-hotplug eth0
iface eth0 inet manual

auto wlan0
iface wlan0 inet manual
     wpa-debug-level 2
     wpa-ssid POTATONET
     wpa-psk XXXXXXXXX
     pre-up iw dev wlan0 set 4addr on
     pre-up iw dev wlan0 set power_save off

allow-auto br0
# iface br0 inet dhcp
iface br0 inet manual
     # bridge_ports wlan0
     bridge_ports none
     bridge_stp off
     bridge_waitport 0
     bridge_fd 0
     # wpa-iface wlan0
     # wpa-bridge br0


I bring up wlan0 and br0:

sudo ifup wlan0
sudo ifup br0

At this point, the wlan0 port should be associated to the AP, even 
though I don't have any layer 3 interfaces on the PC yet. If I force a 
re-authentication from the AP it works fine. WPA rekey works fine.

I do this to bridge up the interfaces:
     sudo brctl addif br0 eth0
     sudo brctl addif br0 wlan0

 From this point on, wpa_supplicant stops working correctly. However, 
the bridge works and ethernet frames are being passed between the laptop 
off of PC port eth0 and the OpenWRT AP. Everything is fine until the WPA 
rekey happens and then the wlan0 interface goes down and stops working.

I did a tcpdump to find out what was going on and discovered that once 
the AP asked for re-authentication from the client, no traffic was going 
out of the wlan0 interface on the client PC. This was supported by 
ifconfig TX counters. wpa_supplicant stops replying to the AP on the 
wlan0 interface.

It should be noted at this point that I am aware wpa_supplicant is 
supposed to need the "-b" argument in this kind of setup, which is what 
the commented-out "wpa-bridge" parameter in the "interfaces" file above 
is for, but it didn't work. I verified the arguments given to 
wpa_supplicant were correct via ps:

/sbin/wpa_supplicant -s -B -P /run/wpa_supplicant.wlan0.pid -i wlan0 -b 
br0 -D nl80211,wext -C /run/wpa_supplicant


Additional notes and observations:

Just to be clear, I have inspected the macaddr and arp tables on both 
the OpenWRT AP and the laptop and the MACs are correct. The wireless 
bridging is definitely working as expected. Let me know if you want 
output from these commands, but I don't think they are relevant.

The default WPA rekey timer is every 10 minutes on OpenWRT, but I can 
force the AP to re-authenticate the client by doing this:
ubus call hostapd.wlan0 del_client '{"addr":"34:de:1a:zz:zz:zz", 
"reason":1, "deauth":true, "ban_time":0}'


Finally, here is some debugging output (wpa_supplicant -ddd) from the 
client PC during a failed re-auth with the AP.

http://jmomo.net/files/wpa_probs.txt


What do?

If additional debugging is needed, let me know what to do. If this is a 
Debian package problem, let me know and I'll go open a bug there.